1. Field of the Invention
The present invention relates to a chemical vapor phase growth method and a chemical vapor phase growth apparatus for performing the method.
A silicide of a heat-resistant metal is used as a material which can maintain the wiring of a micropattern required of a high-density semiconductor integrated circuit at low electrical resistance and which can provide stable wiring producing neither resistance increase nor disconnection, which is caused by migration of atoms.
2. Description of the Related Art
A typical example of such a silicide is tungsten silicide, and a thin film thereof is generally formed by a chemical vapor phase growth or so called chemical vapor deposition (CVD) method. For example, a silicon wafer is heated to a temperature of hundreds of centi degrees (.degree.C.) in a chamber which is evacuated to vacuum, and then silane (SiH.sub.4) and tungsten hexafluoride (WF.sub.6) are introduced into the chamber. As a result, tungsten silicide (WSi.sub.2) is deposited on the silicon wafer. The tungsten silicide WSi.sub.2 is possibly formed by the following reaction: EQU 2SiH.sub.4 +WF.sub.6 -WSi.sub.2 +6HF+H.sub.2
The resistance of the tungsten silicide film formed by the above chemical vapor phase growth method varies with batch. As a result of follow-up investigation of the above phenomenon, the inventors obtained the following finding:
1) A chemical vapor phase growth apparatus in which air is introduced for every batch produces small differences in the film resistance between batches. PA0 2) An apparatus in which chemical vapor phase growth is successively performed for a plurality of batches without introducing atmospheric air into the chamber produces an increase in the film resistance with an increase in the batch number, as shown in FIG. 4. PA0 3) In the apparatus 2), the partial pressure of water vapor in the chamber decreases with an increase in the batch number, as shown in FIG. 3. PA0 4) A difference in the film resistance is mainly caused by a difference in the thickness of the tungsten silicide film.
FIGS. 3 and 4 will be described in detail later.
The inventors estimated from the above finding that an increase in the resistance of a tungsten silicide film is due to a change in the growth speed of the tungsten silicide film, which is caused by a change in the amount of the water vapor remaining in the chamber of the chemical vapor phase growth apparatus used.